This invention relates to the burnishing of internal and external screw threads. The term “burnishing”, as applied to screw threads, means the smoothing out and inwardly deepening of the root surfaces of the screw thread. Screw thread burnishing is typically employed to cold roll and plastically deform the root areas to substantially eliminate stress cracks in the roots which might otherwise cause threaded joint leakage or failure in high stress applications such as in the threaded-together tubular structures utilized in deep downhole fluid recovery systems.
While the desirable results of screw thread burnishing are well known, conventional burnishing equipment and techniques have typically been difficult and complicated—particularly with respect to supporting the work piece (such as a threaded tubular collar for downhole applications) and the thread burnishing equipment. As but one example, a primary difficulty is typically encountered in preventing the imposition of undesirably large net burnishing forces on the work piece (when, for example, it is chucked into a lathe)—a process normally requiring rather intricate custom designed additional support structure which is difficult and time consuming to fabricate and properly install. Additionally, a variety of custom burnishing structures are typically required for different types and sizes of threaded work pieces.
In both internal and external screw thread applications, a need exists for improved thread roller burnishing apparatus which advantageously overcomes these and other problems, limitations and disadvantages commonly associated with conventional thread burnishing equipment. It is to this need that the present invention is primarily directed.